The term 'MOST NASTY' can be broken down into three crossword solutions: MEANEST (7 letters), SNIDEST (7 letters), and VILEST (6 letters). All three words are adjectives that describe something as being unpleasant, unkind, or cruel. MEANEST implies a lack of kindness or consideration, SNIDEST suggests a sly or cutting remark, and VILEST implies extreme wickedness or depravity. Together, these three words suggest the highest degree of nastiness.